Topic: Any good tricks for restoring the front brake disk on a CB750?

[sixthwisconsin]

Here is the disc from my 72 CB350 four with 6800 miles before I sent it off to https://truedisk.net/:


And here it is afterwards:

Very happy with the results! 

Hooray!  My first post on SOHC/4!

That is really nice!!

I would like to ask for opinions as to thinning these beyond the 6mm min spec. Most modern disks are around 4mm+- and other offerings on this forum are thinned to 4mm as well as drilled. They are much lighter and I personally have run them with no issues but not in a racing or high use environment. Very curious as to the opinions here on thinning these beyond 6mm Honda spec of the day.

[seanbarney41]

The 6mm spec is wayyy overbuilt...certainly does not need to be that thick.  These rotors are virtually indestructable.  I had mine thinned by Goddfrey's Garage.  I believe he takes them down to 4mm.  Goddfrey's drilling pattern is much more period looking imo also and a lot more holes.  All this has been used for several thousand miles of hard use on Michigan back roads on my F0.  Why not support a forum member and get same or better service?

[calj737]

The 6mm spec is wayyy overbuilt...certainly does not need to be that thick.  These rotors are virtually indestructable.  I had mine thinned by Goddfrey's Garage.  I believe he takes them down to 4mm.  Goddfrey's drilling pattern is much more period looking imo also and a lot more holes.  All this has been used for several thousand miles of hard use on Michigan back roads on my F0.  Why not support a forum member and get same or better service?

More holes aren’t necessary, and TrueDisk Blanchard grinds their disks. Not sure how Jeff thins his. But, Tom provides an outstanding service, why not also support him?

[seanbarney41]

The 6mm spec is wayyy overbuilt...certainly does not need to be that thick.  These rotors are virtually indestructable.  I had mine thinned by Goddfrey's Garage.  I believe he takes them down to 4mm.  Goddfrey's drilling pattern is much more period looking imo also and a lot more holes.  All this has been used for several thousand miles of hard use on Michigan back roads on my F0.  Why not support a forum member and get same or better service?

More holes aren’t necessary, and TrueDisk Blanchard grinds their disks. Not sure how Jeff thins his. But, Tom provides an outstanding service, why not also support him?

Godfrey s are also Blanchard ground.  More holes equals less weight.   He is a site supporter and regularly contributes to this forum.

I think I will continue to use goddfrey's.

[Stev-o]

  Goddfrey's drilling pattern is much more period looking...

What period? Not SOHC.  Personally, I don't like the look of drilled rotors on my vintage bikes.   When were they first used, late 70's?

[calj737]

Godfrey s are also Blanchard ground.  More holes equals less weight.   He is a site supporter and regularly contributes to this forum.

I think I will continue to use goddfrey's.

I don’t believe that Jeff does Blanchard grind his disks, at least not according to his website nor from any pictures I’ve seen of his rotors. That is not to say he doesn’t do perfectly good work also, but merely a distinction between how TrueDisk machines their rotors.

[seanbarney41]

Jesus ducking christ!..?  Try to encourage support of a forum member and what do you get? 

Cal, why don't ya pm Godfrey and ask him ...kinda nice how being a forum member works like that.

Steveo, check my quote...pretty sure I said MORE period correct...as in closer to...and i am perfectly happy to leave my rotors as is too.  These are not gonna warp, groove deeply, break or bend unless you run over them with a Mack truck.

[calj737]

Jesus ducking christ!..?  Try to encourage support of a forum member and what do you get? 

Cal, why don't ya pm Godfrey and ask him ...kinda nice how being a forum member works like that.

Steveo, check my quote...pretty sure I said MORE period correct...as in closer to...and i am perfectly happy to leave my rotors as is too.  These are not gonna warp, groove deeply, break or bend unless you run over them with a Mack truck.

On the other hand, why don’t you take a Xanax, Whack. No one is disparaging or discouraging doing business with Jeff. Yeas, he’s a member, and offers valuable input often. I’ve done business happily with him.

There’s a significant distinction between something that’s Blanchard ground, and something that isn’t. As I said, I don’t believe per his own website that he does use that process, but does reference machining on a lathe. Perfectly suitable method. Different, but suitable.

So pull your head out and move along. If you’re mistaken, it’s no big deal, we are all human. 

[Bankerdanny]

The Godffrey thinned and drilled front disk on my 550F held up great hauling my ~240lbs plus gear up and down the Colorado mountains and the 300 turns on the Coronado Parkway in Arizona. So I would also agree that the thinner rotor isn't an issue. He also installed new stainless nuts and bolts for the disk to the center hat and offers a service to counter sink the bolt heads to make fitting up a 2nd front disk easier.

Since he is relatively local to me (about 90 miles) I picked it up in person from him and got a tour of his shop (he contracts out the actual surfacing to a local machinist).

[calj737]

The Godffrey thinned and drilled front disk on my 550F held up great hauling my ~240lbs plus gear up and down the Colorado mountains and the 300 turns on the Coronado Parkway in Arizona. So I would also agree that the thinner rotor isn't an issue. He also installed new stainless nuts and bolts for the disk to the center hat and offers a service to counter sink the bolt heads to make fitting up a 2nd front disk easier.

Since he is relatively local to me (about 90 miles) I picked it up in person from him and got a tour of his shop (he contracts out the actual surfacing to a local machinist).

I think everyone has favorable things to say about Jeff and his services.

[Bankerdanny]

I don't think you can go wrong with either service. Like Sean I try to throw business to members when possible, but in terms of quality of work I wouldn't hesitate to use either one.

[sixthwisconsin]

Both services look great and I would have no problems using either.

I have Godffrey roters on two of my bikes with twin disc set up and I like them very much. I was just curious as to opinions on thinning the 7mm Honda rotors to 4mm. Personally, I don't have an issue with it as others have stated. Both of my bikes are on Godffrey's gallery for the product and I do believe they are Blanchard ground but I can't confirm that. I don't have a lot of mileage on either of them after conversion but I have no reason to think there will be a problem.

I really was just trying to spur on conversation about thinning vs not thinning.

Here are my Godffrey disks:

[Can550]

I simply got mine vapor blasted. Initially wanted it to be blasted to paint, now considering to leave it as it is




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[calj737]

It will promptly rust. Paint it or powder coat the center.

[seanbarney41]

I think what mister calj meant is it will corrode, although it may be years before you ever see it, as it is aluminum.
  The actual rotor is made from a stainless alloy that will not rust in our short lifetimes.

[Can550]

It will promptly rust. Paint it or powder coat the center.

Will powder coat !


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[calj737]

My mistake, always thought they were steel. Guess I need to get an SOHC on the lift and put these more modern bikes away 

Aluminum will oxidize if left unprotected. Vapor blasting peens the surface, so it’s more durable and resistant to noticeable oxidation, but it has already begun oxidizing. You can hold it at bay with some products, or clear coat it, or clear powder coat it. Given its location, it’s a drag to keep clean if you ride the bike in any inclement weather.

[Can550]

Clear powder coating is good idea but think will go with black keeping its stock looks


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[SohcCBs]

Go with dual disks:

http://www.salocal.com/sohc/tech/dual_disks/dual_disks.htm

[754]

The carrier is forged aluminum, not a major corrosion issue where you like..
If not stock, gold paint makes them look exoticer.....
 New word for the Dickshunary..

[markb]

I’ve been experimenting with different methods to duplicate the original appearance of the brake disks and haven’t been real happy with the results. The sanding method worked OK if you just want freshen up the appearance which is plenty good for most users. But to be considered restored it’s understandably not there. The Blanchard ground finish looks great but not original so I decided to try to get them done on a surface grinder. I found a shop that said they would try it but quoted me $200 each for six of them, which I think actually wouldn’t be a bad price for one but to do just one would be more. Here is one of my disks that had 1/8” turned off the mounting surface on the back (I think for a dual disk setup) so I’m probably not going to use it for anything and figured it would OK to experiment with.


I decided to make a motorized turntable that I could put on a surface grinder. Fortunately I have access to one at my company’s shop. I scrounged the materials and a few of the parts around the shop and bought the rest and have been working on it on and off the last couple of weeks. At this point I have less than $200 into it if you don’t count the labor. The hardest part was getting the turntable indicated in so it was flat and parallel. I think it turned out pretty good. I even planned ahead and have a dresser mounted (idea from member kmb69, thanks Keith) so I don’t have to remove the tool to redress the wheel.


Here it is on the grinder.


Here is a before pic…


…and after. I ended up grinding about 0.005” off. Still a few grooves and pits in the surface but pretty pleased with the results. I have a NOS K1 disk and the finish on it is rougher than my test piece. I am going to try a courser wheel to see how that looks. It should grind faster and not load up the wheel as much too. I’ll try that on the other side and report back with my results.

[MauiK3]

Mark
Great tool making! Looks like a really good finish. Also looks like a business opportunity, as if you need one with all your other things going.
Is the stone full width? Hard to tell from the photo.
Sure would be fun to see a photo of how they did it back in the day at the factories.

[kmb69]

Mark,
That's awesome! Anxious to see the other side.
Keith

[markb]

Mark
Great tool making! Looks like a really good finish. Also looks like a business opportunity, as if you need one with all your other things going.
Is the stone full width? Hard to tell from the photo.
Sure would be fun to see a photo of how they did it back in the day at the factories.

Thanks. I thought about that but so far this first one took a while and I'm only half done.  Maybe the pace will pick up once I get it down.
The wheel is 3/4" wide. They would have to been done similar to this to get the look they had.

Mark,
That's awesome! Anxious to see the other side.
Keith

Thanks. You were my inspiration. 

[markb]

I’ve finally finished restoring one brake rotor. I think it turned out pretty good. I got three of six ground. I masked and painted one for now. The masking was a challenge because of the spokes and the rivets on the inside.

I tried different tapes and trimming with an exacto knife but couldn’t get decent results. I finally made a tool that has a hole the same size as the diameter of the rivet with a flat land around it.

Then I drilled the same size hole on the other end and machined an angle to make it sharp.


After trying masking tape, vinyl tape and some others I found that the tape that worked the best was duct tape. The flat end of the tool formed the tape around the rivet head.


Then the sharp end trimmed the tape perfectly.


Here’s a pic of the finished product on the outside…


…and the inside.


The only thing I don’t like is that the area that is turned where the rivets are on the outside was originally blueish in color, presumably from getting hot during machining. All of my disks had enough corrosion that had to be removed so there was no saving the blue. I thought maybe using some gun bluing might work but no luck with that so I left it alone.